An intake manifold has a negative pressure tank, which accumulates negative pressure generated in the intake manifold. The negative pressure in the negative pressure tank is applied to a butterfly valve apparatus for communicating and blocking a passage in the intake manifold.
According to U.S. Pat. No. 6,997,157 (JP-A-2005-2942), for example, a negative pressure tank is provided to a space around an intake manifold, thereby sufficiently securing a volume of the negative pressure tank. In this structure, the negative pressure tank can be located in the vicinity of the intake manifold, so that the intake manifold can be formed integrally with the negative pressure tank. Thus, the number of components of the intake manifold can be restricted.
However, in an intake manifold used for an engine such as V-type engine, it is difficult to secure a space sufficiently for accommodating a negative pressure tank having a large volume around the manifold. When a negative pressure tank is not formed integrally with an intake manifold, and the negative pressure tank is distant from the intake manifold, components for constructing the negative pressure tank and for communicating the negative pressure tank with the intake manifold need to be additionally provided. As a result, the number of components increases.